It is widely recognised that wound pain is one of the major problems associated with wounds or ulcers. Wounds are by definition divided into two categories: Acute and chronic wounds. Acute wounds may be wounds such as burns and surgical wounds, while chronic wounds may be in the form of pressure sores, leg ulcers and diabetic ulcers. Pain can be associated with both chronic and acute wounds although the influence on patients well-being will be more pronounced when the wound is chronic.
Pain can be divided into three categories: Acute pain, non-malignant pain and cancer pain. Wound pain will often be either acute or non-malignant dependent on the character of the actual wound and whether the wound is being manipulated or not e.g. during a dressing change. Furthermore, the pain will in general have nociceptive or neurogen origin.
Furthermore, wound pain can be sub-divided into three classes: Non-cyclic acute wound pain, which may occur during for instance at debridement of necrotic tissue in a wound or removal of drainage;                Cyclic acute wound pain, which may occur during for instance dressing changes or in some cases debridement; and        Chronic wound pain, which is a persistent pain that can occur even without manipulation of the involved skin or tissue, i.e. pain between dressing changes.        
In the following we will primarily address relief of the persistent pain or the chronic pain associated with wounds between dressing changes. However, treatments suitable for this purpose may also be able to relieve pain during dressing change and debridement as described below.
Pain in itself is of course a major discomfort for the patient and will therefore affect patients quality of life. In addition, pain stimulates catecholamine release and as a result of that local vasoconstriction arises and a reduced oxygen supply to a cutaneous wound will occur. This may affect wound healing and resistance to infection of the wound. Furthermore, wound healing may also be delayed due to the general influence pain may have on the patient, such as loss of appetite, less mobility, worse overall condition and lack of enthusiasm. However, the possible effect of pain on wound healing has not been proven in the literature and is therefore speculative. In contrast, it is well recognized that pain has an impact on the health related quality of life (HQOL) for patients.
Wound pain has proven to be decreased by modern moist wound healing principles. Moist wound healing dressings keep the environment under the dressing moist but are at the same time capable of absorbing considerable amounts of exudate from the wound, in order to protect the periulcer skin and to avoid leakage. During the wear time of a moist wound healing dressing, tissue and nerve endings remain moist. Such dressings, e.g. hydrocolloid dressings will be soothing and less painful than traditional dry gauze dressings during application and in situ. Debridement will often also be less painful as the wound bed will be kept in a moist condition and thus no painful drying out is seen.
Although moist wound healing has been proven to improve healing rates, relieve pain in situ, prevent the wound bed from drying out, decrease the discomfort with wound debridement, and overall, improve the quality of life for the patient, added benefits, in terms of a more direct way of addressing the local wound pain between dressing changes associated with wounds is still needed.
It is well known in the art to incorporate analgesics or anaesthetics into topical products for treatment of pain or to produce anaesthesia in intact skin surfaces or systemically in the body. These products may be in the form of trans-dermal dressings or patches, creams, gels or ointments. In order to enhance the rate at which the drug passes through the skin to reach the systemic circulation from e.g. the trans-dermal patch or to achieve an appropriate formulation for intact skin surfaces it is often desirable or even necessary to incorporate other components. These components will interfere with an open wound setting in terms of producing possible irritation, sensibilisation or even toxicological effects in the open wound setting and to the often very fragile periulcer skin around the open wound.
In International Patent Application No. WO 94/23713 is disclosed a trans-dermal anti-inflammatory compositions. The compositions may be used for topical and trans-dermal application, such as ointments and dressings and the anti-inflammatory composition is preferably NSAIDs (non-steroid anti-inflammatory drugs).
However, delivering drugs to intact healthy skin and to the systemic circulation is very different from delivering drugs locally to open wounds or damaged skin. The skin provides an effective barrier between the drug and the underlying tissue and blood circulation in trans-dermal delivery, and therefore, the drug has to be formulated in such a way that it is capable of overcoming this barrier. Also the concentration of the drug in the trans-dermal formulation has to be higher in order to overcome the skin barrier and reach the systemic circulation in a plasma concentration high enough for systemic effect. A wound is provided with little or no barrier, and furthermore, the wound will often exudate and may be contaminated.
Furthermore, a wound dressing often needs to be provided with wound exudates handling means, in order to give optimal comfort for the patient. The barrier for the release of the drug for local administration to an open wound will be the medical device, and not the intact skin. The medical device may absorb and retain the exudate from the wound, and therefore prevent the maceration of the surrounding skin and wound tissue that is often fragile and vulnerable. As a result, the wound management and patient comfort is increased. A trans-dermal patch, or a topical cream, or ointment will not be able to handle wound exudate. Neither the adhesive, nor the other components of the patch may be designed for an open wound setting and for contact with the very fragile skin surroundings. Also, the drug concentration in a trans-dermal system or a topical ointment, gel or cream may be too high to be used in an open wound where no absorption barrier is seen. Furthermore, additives such as penetration enhancers, comprised in the creams, gels or ointments or trans-dermal patches will make them unsuitable for use in an open wound, as these additives often are too aggressive, or even toxic for introducing directly into an open wound.
Most wound care products are prepared without such additives as these additives may interfere with the wound healing and influence the well being of the patient. Examples are hydrogels made especially for e.g. debridement in open wounds and for application under a dressing and other devices for moist wound healing like dressings comprising foams, alginates or hydrocolloids.
A controlled release of drugs is often desired both in trans-dermal delivery and open wound treatment. However, the release mechanisms may be quite different in the two systems. In a trans-dermal device such as a patch, cream, ointment or gel, the skin barrier may serve as the controlling release layer. The additives may further control the release. In a wound care device, the release may be controlled in other ways, e.g. by the amount of exudate from the wound, or by using controlled release matrices.
Analgesics generally can relieve pain in open wounds without seriously interfering with the sense perception. In contrast, anesthetics interfere with sense perception when applied locally, and can result in loss of consciousness when used systemically. Loss of sense perception in a wound and surroundings is considered to be not acceptable because the patient loses the ability to feel possible injury and change in the wound. Therefore it may be preferred to use analgesics in order to relieve wound pain over a longer period.
In U.S. Pat. No. 6,312,713 is disclosed a thin-layered dressing for surface wounds which gradually releases drugs, such as analgesics. The drug is incorporated in a hydrophilic polymeric matrix and may be used topically. The dressing is thin and does not comprise wound exudates handling means, and will thus only be suitable for dry wounds.
U.S. Pat. No. 5,792,469 a in situ forming film dressing with therapeutic agents such as pain relieving agents. The film is sprayed onto the desired body part. The dressing is only suitable for dry wounds, as no wound exudates handling means are included.
In U.S. Pat. No. 6,048,850 is disclosed a method of selectively inhibiting PGHS-2 in a human host. The reference is silent with respect to local wound treatment.
U.S. Pat. No. 6,190,689 discloses a trans-dermal device comprising a hot-melt adhesive with an incorporated substance. The use of pain relieving agents in the treatment of wounds is mentioned, but the reference is silent with respect to any details or examples to this subject.
In International Patent Application No. WO 00/07574 is disclosed medicinal products with retarded pharmacological activity. The products are primarily intended for use in catheters, though use in wound care devices is mentioned.
Thus, there is still a need for a medical device addressing superior wound management as well as local pain relief in terms of addition of analgesic compounds. Such a wound care device is achieved by the present invention combining the beneficial effects of moist wound healing with the pharmacological effects of a pain relieving agent, that supply pain relief locally to a wound and nearby surroundings but not systemically i.e. in the body.